Morphology And Properties Of Composites Based On Polypropylene Or Nylon11

Polypropylene (PP) is one of the biggest number of general plastics. It has many desirable properties, such as: good lucency, low density (0.89g/cm3~0.91g/cm3), heat endurance (Tm = 160℃, and it can be used in long time at 100 ~ 120℃), favorable mechanical properties, low cost, innocuity, excellent acid-resistant properties, excellent reactance, facile processing and recycle characterties, good pucker resistance and rigidity because of its higher crystallinity. Therefore, PP is widely used in the field, such as machine (accessory), chemistry industry (container, synthesizer), electrical industry and transport. However, the poor impact properties, especially at the low temperatures, limit some of its applications. Hence impact toughening of PP has gained much attention in recent years.Impact toughening of PP with various types of elastomers has been approved to be a most useful method. Among the impact modifiers commonly used for PP, ethylene-propylene-diene terpolymers (EPDM) have been considered the most effective ones, PP/EPDM has excellent properties of high temperature and impact. However, high cost and complex synthetic technics of EPDM, limit some of its applications in civil. To reduce cost, we try to enhance impact toughening of PP with syndiotactic1,2-polybutadiene (s-PB) of low crystallinity and low syndiotactic degree. In addition, considering the compatibility and interaction of interface, the molecular structure of PP is similar to that of s-PB, their main chains are the same. For the case of side chain, PP is methyl and s-PB is ethylene. Based on the principle that more similar material has more compatibility, PP and s-PB should have good compatibility. The interface in different phase can enhance the toughening property of PP.The PP/s-PB composites studied in this dissertation have been prepared by melt compounding. The purpose of this dissertation is to study the rheological behavior, crystallization, mechanical properties, dynamic mechanical properties and microstructure. It is well known that the physical properties of materials depend on their microstructure, thus, investigation of the microstructure and macro-properties of polymer blends are important both theoretically and practically.It is well known that syndiotactic1,2-polybutadiene is very easy to crosslinked at high temperature due to a number of double bonds on the side chain. We have investigated the relationship between experimental temperature and crosslinked reaction by rotational rheometer. Three crosslinking reaction temperatures for this experiment have been detected firstly that the temperature of 137℃can be defined as initial crosslinking temperature, the temperature of 160℃is crosslinking reaction temperature, the temperature of 207℃is rapidly crosslinking reaction temperature. When the temperatures are lower than 160℃, the material viscoelasticity is stable in 25 minutes.Studying the rheological behavior of PP/s-PB composites, it is found that the range of strain is less than 8% in linear elastic region, and the shearing-thin phenomena in the higher strain region is more and more unconspicuous. This is the result of the two macromolecular interaction of polymers. At high processing temperature (above 240℃), because crosslingking reaction easily takes place in high temperature, this might lead to high viscous of s-PB, phase separation easily happens in the composite system. Furthermore, the end region of G′and G′′of the composites is flat, and the phenomena will shift to high frequency region as the content of s-PB increases. This is also leaded by the crosslingking of s-PB as shearing time increasing. When the content of s-PB is above 10%, viscosity of the composites increases as the content of s-PB increases. When the content is below 10%, s-PB distributes in PP as particles, which can be considered as enhancement phase. Thus, the interaction of the particles leads to the enhancement of viscosity. The crystallization and melting behavior, isothermal crystallization kinetics and nonisothermal crystallization kinetics of the PP/s-PB composites are studies. It has been found that the adding of s-PB in the matrix has remarkable influence on the crystallization and melting behavior of PP/s-PB composites. According to Nishi and Wang theory, the PP/s-PB composites are thermodynamically immiscible, but the system are blended compulsively by mixer, might still achieve the uniform mixed effect and stable blending system in macroscopicy. When the content of s-PB is low, the crystallization temperature and crystallization rate of PP all increase, the super-cooling temperature of PP reduce, the incorporation of s-PB has nucleation effect on PP, whereas, the degree of crystallinity of PP decrease, this indicates that the low incorporation of s-PB has obviously effect on PP crystallinity. With the content of s-PB increasing, the degree of crystallinity of PP decreases slightly further. When s-PB becomes the continuous phase in the system, the degree of crystallinity of s-PB decreases with the content of PP increasing. The balanced melting point of PP/s-PB composites decreases with the content of s-PB increasing, this indicates that the two phases have strong interaction. As the case of the PP/s-PB composites, the half time of crystallization ( t1 /2) increases with the crystallization temperature increasing and accords with index relation, suggesting that the nucleating effect becomes difficult with the crystallization temperature increasing. With the content of s-PB increasing, the half time of crystallization decreases, more improving the nucleating effect of s-PB. Avrami equation is applicable for the isothermal crystallization of the PP/s-PB composites. The linear segment of curve is nearly parallel, indicating that the nucleating mechanism and grow method of PP are similar. From crystallization initially to high relative crystalline, the lg{? ln[1?X(t)]}- lg t curve remains linear, suggesting that modified Avrami equation correctly describes the nonisothermal crystallization process of PP and PP/s-PB composites. The nonisothermal crystallization activation energies of PP is higher than that of PP/s-PB composites.The studies of the mechanical properties of the PP/s-PB composites system are carried on, the results indicate that the tensile modulus rises initially and reduces with the s-PB loading increasing. When the content of s-PB is 10%, the tensile modulus of the composites is higher (771MPa) than that of neat PP (606MPa), when the content of s-PB is 20%, the tensile module of the composites is similar (589MPa) to that of neat PP. This indicates when the content of s-PB is lower, the PP/s-PB composites is enhanced by s-PB. The tensile strength, flexural modulus, flexural strength and hardness decrease with the content of s-PB increasing. The impact strength at 23℃and at 0℃all increase with the content of s-PB increasing, the maximum value is 12.9kJ/m2 (40wt% at 23℃) and 7.9kJ/m2( 50wt% at 0℃), they are 339%, 316% and one fold higher than those of the neat PP, respectively. There are obvious brittle-ductile transition ranges in normal temperature impact testing and low temperature impact testing.Analysis of the dynamic mechanical properties of PP/s-PB composites show that the dynamic storage modulus ( E′) of composites lie in between that of PP and s-PB, and the E′value decreases with the content of s-PB increasing. This is due to the E′value of s-PB is lower than that of PP. The loss angle factor ( Tanδ) value increases with the content of s-PB increasing. Single peak can be observed in the curves of Tanδversus temperature, the temperature of the peak located is the glass transition temperature ( Tg ). The glass transition temperature ( Tg ) of the composites shifts to lower temperature with the content of s-PB increasing. According to the compatible theory between two components, the two phases is partly miscibility, but because the differences of the two polymer's glass transition temperature ( Tg ) are too small, in curves of Tanδversus temperature, the single peak possibly is overlap of two independent peak. Therefore, we thought that the PP/s-PB blends possibly are between complete miscibility and complete immiscibility.The morphological characteristics of the PP/s-PB composites are illustrated in the SEM micrographs show that when the s-PB concentration is lower than 30wt% (containing 30wt%), the shapes of the s-PB dispersed phase are spheric or oval. When the s-PB content is 40wt% and 50wt%, the composites show doubling continuous phase shape, that is so-called"sea - sea"structure. When the s-PB content is higher 60wt% (containing 60wt%), the dispersed phase and continuous phase reversed, the shapes of the PP dispersed phase are spheric or oval in s-PB matrix. The SEM micrographs of the fracture surface of specimens after impact testing demonstrated that the surface of Pure PP is smooth and showed obvious brittle fracture, whereas, when s-PB is added, the fracture surface of specimens after impact testing is ductile, the interface of polymer is a certain compatibility, the interface of crossing section place show the obvious plastic deformation and demonstrated the ductile fracture characteristic.Polymer/clay nanocomposites have aroused considerable concerns from both industrial and academic circles in recent years. The layer-structured clay is naturally hydrophilic. They become organophilic by modifying the silicate surfaces with organic cations by ion exchange reaction. The organoclay thus obtained has been incorporated into a variety of polymeric matrices successfully by in-situ polymerization, melt or solution blending. The resulting nanocomposites show significantly enhanced mechanical properties, dimensional stability, permeability, and fire-resistance relative to the counterpart polymers. Therefore, the polymer/clay nanocomposites have been found wide applications in automotive industry, packaging, aerospace, and some commercial products are now available in the market. The thermal stability of the nanocomposites is improved by about 20℃when the clay loading is lower than 4wt%. Compared with neat PA11, a significant increase of 100% in the storage modulus for the nanocomposite containing 8wt% clay is reported. The exfoliated nanocomposites are obtained for lower clay loadings and the intercalated ones dominate (by coexisting with some delaminated platelets) for higher clay contents. The main aim of this study is to investigate the effect of adding clay on the rheological properties of PA11 matrix, as well as a relationship between clay morphology and rheology of nanocomposites.Clay morphology throughout the polymeric matrix is illustrated by TEM for PA11 and PA11/clay nanocomposites. Clearly, at lower clay loading (e.g. 2wt%), a disordered and exfoliated clay nanostructure is observed, whereas at higher clay concentration (e.g. 5wt%), a typical ordered intercalated nanoclay morphology is seen. The ordered nanoclay stacks are responsible for the abnormal dependence of both linear and nonlinear viscoelastic responses. Compared with neat PA11, though all PA11/clay nanocomposites exhibit much higher G′, G′′and shear viscosities, the plateaus in G′andG′′at low frequencies are not observed. In addition, the nanocomposite generally obey the type-ⅠCox-Merz rule, which is useful to estimate shear viscosities at higher shear rates from the dynamic data. However, the type-Ⅱis not applicable to all the samples studied here.